Abstract
This paper reviews our current understanding of the acceleration mechanism of anomalous cosmic rays (ACRs). ACRs were first discovered in the early 1970s and soon afterwards it was recognized that they were accelerated interstellar pickup ions that obtained most of their energization in the outer heliosphere. Their observed composition and charge state suggest they are accelerated to over 200 MeV total energy in about a year. Diffusive shock acceleration at the solar-wind termination shock, which provided a natural explanation for spacecraft observations prior to the Voyager crossings of the termination shock in 2004 and 2007, was the long-held paradigm for the acceleration mechanism. But when both Voyagers crossed the shock, the ACR energy spectrum remained modulated, suggesting a source more distant than the shock. While shock acceleration remains a popular mechanism, other ideas have emerged recently to explain the observations. This review focuses on three main acceleration mechanisms that have been proposed: (a) acceleration at the termination shock including new effects such as the global blunt-shape of the shock and large-scale turbulence, (b) acceleration by magnetic reconnection in the heliosheath, and (c) acceleration by diffusive compression acceleration in the heliosheath.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
Notes
A heliosheath flow of 100 km/s times 13 days translates to around 2/3 of an AU.
The kinetic energy, T, of a particle with charge, q, drifting a distance, L, along an electric field, E, is T=qEL. Taking the electric field to be C A B/c, where B is the heliosheath magnetic field strength (about 10−6 nT), and C A is the heliosheath Alfven speed (about 40 km/s) and assuming a maximum energy of T=200 MeV, then we find L≈5×1015 cm, which is over 300 AU
References
J.H. Adams, M.D. Leising, In: Proc. 22nd ICRC vol. 3, p. 304 (1991)
J.H. Adams, L.P. Beam, A.J. Tylka, Astrophys. J. 377, 292 (1991)
W. Axford, E. Leer, G. Skadron, In: Proc. 15th ICRC vol. 11, p. 132 (1977)
A.F. Barghouty, J.R. Jokipii, R.A. Mewaldt, AIP Conf. Proc. 528, 337 (2000)
A.R. Bell, Mon. Not. R. Astron. Soc. 182, 147 (1978)
J. Birn et al., J. Geophys. Res. 106, 3715 (2001)
R.D. Blandford, J.P. Ostriker, Astrophys. J. 221, 29 (1978)
S.N. Borovikov, N.V. Pogorelov, L.F. Burlaga, J.D. Richardson, Astrophys. J. Lett. 728, 21 (2011)
L.F. Burlaga, N.F. Ness, Astrophys. J. 1, 311 (2009)
L.F. Burlaga, N.F. Ness, Astrophys. J. 737, 35 (2011a)
L.F. Burlaga, N.F. Ness, J. Geophys. Res. 116, 05102 (2011b)
L.F. Burlaga, N.F. Ness, J.D. Richardson, J. Geophys. Res. 108, 8028 (2003)
L.F. Burlaga, N.F. Ness, M.H. Acuna, R.P. Lepping, J.E.P. Connerney, E.C. Stone, F.B. McDonald, Science 5743, 2027 (2005)
L.F. Burlaga, N.F. Ness, M.H. Acuna, R.P. Lepping, J.E.P. Connerney, J.P. Richardson, Nature 454, 75 (2008)
P. Cassak, M.A. Shay, J.F. Drake, Phys. Rev. Lett. 95, 235002 (2005)
A.C. Cummings, E.C. Stone, F.B. McDonald, B.C. Heikkila, N. Lal, W.R. Webber, AIP Conf. Proc. 1039, 343 (2008)
R.B. Decker, S.M. Krimigis, E.C. Roelof, M.E. Hill, T.P. Armstrong, G. Gloeckler, D.C. Hamilton, L.J. Lanzerotti, Science 309, 2020 (2005)
R.B. Decker, S.M. Krimigis, E.C. Roelof, M.E. Hill, T.P. Armstrong, G. Gloeckler, D.C. Hamilton, L.J. Lanzerotti, Nature 454, 67 (2008)
J.F. Drake, M. Swisdak, H. Che, M.A. Shay, Nature 443, 553 (2006a)
J.F. Drake, M. Swisdak, K.M. Schoeffler, B.N. Rogers, S. Kobayashi, Geophys. Res. Lett. 33, 13105 (2006b)
J.F. Drake, M. Opher, M. Swisdak, J.N. Chamoun, Astrophys. J. 709, 963 (2010)
J.A. Earl, J.R. Jokipii, G. Morfill, Astrophys. J. 331, 91 (1988)
D.C. Ellison, D. Eichler, Astrophys. J. 286, 691 (1984)
L. Fisk, G. Gloeckler, Astrophys. J. 640, 79 (2006)
L. Fisk, G. Gloeckler, Astrophys. J. 686, 1466 (2008)
L. Fisk, G. Gloeckler, Adv. Space Res. 43, 1471 (2009)
L. Fisk, G. Gloeckler, Astrophys. J. 720, 533 (2010)
L. Fisk, M.A. Lee, Astrophys. J. 237, 620 (1980)
L. Fisk, G. Gloeckler, T.H. Zurbuchen, Astrophys. J. 644, 631 (2006)
L. Fisk, B. Kozlovsky, R. Ramaty, Astrophys. J. 190, 35 (1974)
V. Florinski, R.B. Decker, J.A. le Roux, G.P. Zank, Geophys. Res. Lett. 36, 12101 (2009)
P.C. Frisch, Space Sci. Rev. 78, 213 (1996)
M. Garcia-Munoz, G.M. Mason, J.A. Simpson, In: Proc. 13th ICRC vol. 2, p. 1304 (1973)
J. Giacalone, Astrophys. J. 628, 37 (2005)
J. Giacalone, Heliophysics: Space storms and radiation, in Causes and Effects, ed. by C.J. Schrijver, G.L. Siscoe (Cambridge University Press, Cambridge, 2010), p. 233, Chap. 9
J. Giacalone, D. Burgess, Geophys. Res. Lett. 37, 19104 (2010)
J. Giacalone, R.B. Decker, Astrophys. J. 710, 91 (2010)
J. Giacalone, J. Jokipii, Astrophys. J. 649, 137 (2006)
J. Giacalone, J.R. Jokipii, J. Kóta, Particle acceleration in astrophysical plasmas, in Geospace and Beyond, ed. by D. Gallagher, J. Horwitz, J. Perez, R. Preece, J. Quenby (Am. Geophys. Union, Washington, 2005), p. 41
J. Giacalone, J.R. Jokipii, J.E. Mazur, Astrophys. J. 532, 75 (2000)
J. Giacalone, J. Jokipii, J. Kota, Astrophys. J. 573, 845 (2002)
J. Giacalone, D. Burgess, S.J. Schwartz, D.C. Ellison, Geophys. Res. Lett. 19, 433 (1992)
G. Gloeckler, L.A. Fisk, Astrophys. J. 648, 63 (2006)
F. Guo, J.R. Jokipii, J. Kota, Astrophys. J. 725, 128 (2010)
D. Hovestadt, O. Vollmer, G. Gloeckler, C.Y. Fan, Phys. Rev. Lett. 31, 650 (1973)
J.R. Jokipii, J. Geophys. Res. 91, 2929 (1986)
J.R. Jokipii, AIP Conf. Proc. 203, 155 (1990)
J.R. Jokipii, Astrophys. J. 393, 41 (1992)
J.R. Jokipii, Astrophys. J. 466, 47 (1996)
J.R. Jokipii, Astrophys. J. 631, 163 (2005)
J.R. Jokipii, J. Kóta, In: Proc. of the 27th ICRC p. 3341 (2001)
J.R. Jokipii, M.A. Lee, Astrophys. J. 713, 475 (2010)
J.R. Jokipii, L.L. Williams, Astrophys. J. 394, 184 (1992)
J.R. Jokipii, J. Giacalone, J. Kota, Astrophys. J. 611, 141 (2004)
B. Klecker, Space Sci. Rev. 72, 419 (1995)
J. Kota, Astrophys. J. 723, 393 (2010)
J. Kota, J.R. Jokipii, AIP Conf. Proc. 1039, 397 (2008)
G. Kowal, E.M. de Gouveia Dal Pino, A. Lazarian, Astrophys. J. 735, 102 (2011)
S.M. Krimigis, R.B. Decker, M.E. Hill, T.P. Armstrong, G. Gloeckler, D.C. Hamilton, L.J. Lanzerotti, E.C. Roelof, Nature 426, 45 (2003)
S.M. Krimigis, E.C. Roelof, R.B. Decker, M.E. Hill, Nature 474, 359 (2011)
G.F. Krymsky, Dokl. Akad. Nauk SSSR 234, 1306 (1977)
A. Lazarian, M. Opher, Astrophys. J. 703, 8 (2009)
A. Lazarian, E.T. Vishniac, Astrophys. J. 517, 760 (1999)
G. Li, G.P. Zank, AIP Conf. Proc. 858, 183 (2006)
J.E. Mazur, G.M. Mason, J.R. Dwyer, J. Giacalone, J.R. Jokipii, E.C. Stone, Astrophys. J. 35, 79 (2000)
D.J. McComas, N.A. Schwadron, Geophys. Res. Lett. 33, 0410 (2006)
F.B. McDonald, J.B. Teegarden, J.H. Trainor, W.R. Webber, Astrophys. J. 187, 105 (1974)
F.B. McDonald, B. Heikkila, N. Lal, E.C. Stone, J. Geophys. Res. 105, 1 (2000)
R.A. Mwealdt, R.S. Selesnick, J.R. Cummings, E.C. Stone, T.T. von Rosenvinge, Astrophys. J. 466, 43 (1996)
M. Neugebauer, J. Giacalone, J. Geophys. Res. 110, 12106 (2005)
M. Neugebauer, J. Giacalone, E. Chollet, D. Lario, J. Geophys. Res. 111, 12107 (2006)
M. Øieroset, T.D. Phan, M. Fujimoto, R.P. Lin, R.P. Lepping, Nature 412, 417 (2001)
M. Oka, T. Phan, S. Krucker, M. Fujimoto, I. Shinohara, Astrophys. J. 714, 915 (2010)
M. Opher, E.C. Stone, T.I. Gombosi, Science 5826, 875 (2007)
M. Opher, J.F. Drake, M. Swisdak, K.M. Schoeffler, J.D. Richardson, R.B. Decker, Astrophys. J. 734, 71 (2011)
E.N. Parker, Planet. Space Sci. 13, 9 (1965)
M. Pesses, D. Eichle, J. Jokipii, Astrophys. J. 246, 85 (1981)
T.D. Phan et al., Geophys. Res. Lett. 34, 14104 (2007)
M.S. Potgieter, H. Moraal, Astrophys. J. 330, 445 (1988)
J.D. Richardson, E.C. Stone, A.C. Cummings, J.C. Kasper, M. Zhang, F.F. Burlaga, N. Ness, Y. Liu, Geophys. Res. Lett. 33, 21112 (2006)
J.D. Richardson, J.C. Kasper, C. Wang, J.W.B.A.J. Lazarus, Nature 454, 63 (2008)
K.M. Schoeffler, J.F. Drake, M. Swisdak, Astrophys. J. 743, 70 (2011)
K.M. Schoeffler, J.F. Drake, M. Swisdak, Astrophys. J. 750, 30 (2012)
M. Scholer, Geophys. Res. Lett. 17, 1821 (1990)
N.A. Schwadron, M.A. Lee, D.J. McComas, Astrophys. J. 675, 1584 (2008)
M.A. Shay, J.F. Drake, M. Swisdak, Phys. Rev. Lett. 99, 155002 (2007)
M.A. Shay, J.F. Drake, R.E. Denton, D. Biskamp, J. Geophys. Res. 25, 9165 (1998)
E.J. Smith, J. Geophys. Res. 106, 15819 (2001)
C.D. Steenberg, H. Moraal, Astrophys. J. 463, 776 (1996)
E.C. Stone, A.C. Cummings, D.C. Hamilton, M.E. Hill, S.M. Krimigis, In: Proc. of the 26th ICRC, vol. 7 (1999) p. 551
E.C. Stone, A.C. Cummings, F.B. McDonald, B.C. Heikkila, N. Lal, W.R. Webber, Nature 454, 71 (2008)
E. Stone, A. Cummings, F. McDonald, B. Heikkila, N. Lal, W. Webber, Science 309, 2017 (2005)
R.D. Strauss, M.S. Potgieter, S.E.S. Ferreira, M.E. Hill, Astron. Astrophys. 522, 35 (2010)
S.I. Syrovatsky, Sov. Phys. JETP 13, 1257 (1960)
M. Yamada, Phys. Plasmas 14, 058102 (2007)
G.P. Zank, Space Sci. Rev. 89, 413 (1999)
M. Zhang, AIP Conf. Proc. 858, 226 (2006)
Acknowledgements
We thank the local organizers of this workshop for their generous hospitality and for organizing a very interesting meeting. The work of JG and JRJ was supported, in part, by NASA under grants NNX10AF24G, NNX11AB45G and NNX11AO64G.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Giacalone, J., Drake, J.F. & Jokipii, J.R. The Acceleration Mechanism of Anomalous Cosmic Rays. Space Sci Rev 173, 283–307 (2012). https://doi.org/10.1007/s11214-012-9915-z
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11214-012-9915-z